This invention relates generally to speed controls for DC fans and particularly to a low cost speed control for a small, brushless "pancake" type DC fan.
With the rapid proliferation of computers and computer related equipment, the small brushless DC fan of "pancake" or flat configuration has proven enormously popular for providing ventilation because of its small size, straight flow through design and installation flexibility. A long recognized problem is that of fan operating noise, which may become objectionable since such fans are generally selected for "worst case" conditions, i.e. to deliver maximum cooling. Often the ambient temperature and/or loading demands on the equipment are such that significantly less cooling is required. Consequently the fan could operate at a lower speed and the operating noise of the fan running at high speed is unnecessarily disturbing.
There have been a number of prior art solutions and attempted solutions to this problem. Motor speed controls, for example, have been available for many years and have been applied in many different environments. Fan speed controls are also well known in the art, although mainly for controlling AC motors. A brushless DC fan motor involves further difficulties in that it loses torque at lower than normal operating voltages and may become very unreliable. Also, prior art control circuits for controlling the speed of a brushless DC fan motor are relatively complex and expensive.
With the invention, a very simple, conpact, DC fan speed control is provided that uses a minimum number of readily available, low cost components. The speed control of the invention may be mounted in inconspicuous places because of its compact size and low heat dissipation. Further, the inventive device reliably controls the speed of the fan over a wide range, while retaining full torque electrical input.